The present invention relates to an improved buffer circuit for use in wideband tuners and, more particularly, to a buffer circuit suitable for use in CATV which receives more than 30 channels of television signals.
The buffer amplifier circuit in a wideband tuner is interposed between a local oscillator and a mixer, and is adapted to amplify the output signal from the local oscillator and to supply the amplified signal to the mixer in matching with the latter. The mixer receives the output signal from the buffer amplifier circuit, i.e. the amplified output from the local oscillator, and a high-frequency wave signal which is being received, and effects a frequency conversion of the high-frequency wave signal into an intermediate frequency signal (referred to as IF, hereinafter).
In the case of a CATV system, for instance, the frequencies of the received signals range between 54 MHz and 300 MHz. Assuming that the IF is to be 378 MHz, the oscillation frequency of the local oscillator is selected to be 432 MHz to 678 MHz.
In general, the local oscillator has a higher output level in the low oscillation frequency range. Therefore, it is often experienced that the output signal from the buffer smplifier is undesirably distorted when the latter receives an output signal from such a local oscillator. This distortion is transmitted from the buffer amplifier to the mixer, affecting adversely the frequency conversion conducted in the mixer.